1. Field of the Invention
This invention relates to a dicing tape attaching method, for attaching a dicing tape on the back surface of a wafer, and to a dicing tape attaching apparatus for carrying out the method.
2. Description of the Related Art
In the semiconductor fabrication field, wafers have increased in size every year, on the one hand, and, in order to increase the mounting density, the thickness of the wafer has been reduced. The thickness of the wafer is reduced by a back grind process which grinds the back surface of the semiconductor wafer. In the back grind process, a surface protective tape is attached on the front surface of the wafer to protect the semiconductor elements formed on the front surface.
FIG. 7 is an enlarged sectional view of a circular wafer with a surface protective film attached on the front surface of the wafer. As can be understood from FIG. 7, the edge portion 25 of the circular wafer 20 is originally chamfered. Also, a surface protective film 11 is attached on the front surface 21 of the wafer 20. As shown in FIG. 7, in the case where the wafer 20 is back ground and reduced in thickness from Z0 to Z1, the chamfered portion 27 on the back surface of the wafer 20 is cut off, and the new back surface 22 (ground surface) of the wafer 20 reaches the chamfered portion 26 of the front surface.
Next, as shown in FIG. 8, the wafer 20 is inverted with the back surface 22 up and arranged in a mount frame 36 somewhat larger than the wafer 20. By moving an attaching roll 146, such as a rubber roll, from one end to the other of the mount frame 36, the dicing tape 3 is attached on both the wafer 20 and the mount frame 36. As a result, the back ground wafer 20 is integrated with the mount frame 36 for an improved handling characteristic of the wafer 20 in the subsequent processes.
FIGS. 9a and 9b are sectional views taken along the attaching roll 146 and shown by the dotted line and the solid line, respectively. Specifically, FIG. 9a shows the state in which the dicing tape 3 begins to be attached at the end portion 28 of the wafer 20. FIG. 9b, on the other hand, shows the state in which the dicing tape is attached to about central portion of the wafer 20. As can be understood from these drawings, the wafer 20 and the mount frame 36 are supported on tables 131, 138, respectively.
As can be understood by reference to FIG. 7, the thickness of the wafer 20 is reduced by back grinding and, therefore, the end portion 28 of the wafer 20 after back grinding corresponds to the chamfered portion 26. At the time of starting to attach the dicing tape 3 as shown in FIG. 9a, therefore, a force is exerted in the direction of arrow in such a way that the central portion, or thereabouts, of the attaching roll 146 is deformed and the chamfered portion 26 of the wafer 20 lacking a surface protective film 11 is pressed. Also, immediately before the end of the process of attaching the dicing tape 3, a similar force is exerted at the end portion 29 opposite of the end portion 28.
Also, at about the central portion of the wafer 20, as shown in FIG. 9b, the attaching roll 146 is deformed at the edges of the wafer 20, and the ends of the wafer 20 perpendicular to the moving direction the attaching roll 146 are curved downward. This force may form cuts or cracks at the ends of the wafer 20, so that the yield of the products is reduced. Even in the case where cuts or cracks do not occur, internal distortions of the wafer is caused and may appear as cuts or cracks in the subsequent processes.
This invention has been achieved in view of this situation, and the object thereof is to provide a dicing tape attaching method in which the dicing tape can be attached on the mount frame and the wafer without forming cuts or cracks or internal distortions of the wafer, and a dicing tape attaching apparatus for carrying out the method.